This invention relates to coil coatings and more particularly to aqueous coil coating primers for coating coil metal stock.
Coil coating primers ordinarily are applied to continuous coils of bare metal stock to protect the uncoated metal prior to fabricating of the primed metal. The bare coil metal first is cleaned of protective oil and thereafter coated with a coil coating primer. The primed, coiled metal stock ordinarily then is topcoated and subjected to a wide variety of fabricating operations and post-forming operations wherein the coiled metal is cut to length, die-formed, roll-formed, or stamped to produce a formed metal object. Due to the wide variety of subsequent fabricating, forming and bending operations, coil coating primers must possess unusual properties in order to withstand the subsequent cutting, bending, stamping, drawing, and the like whereby the integrity and adhesion to the coiled stock is maintained. Accordingly, coil coating primers must have flexibility and adhesion to withstand subsequent bending operations as well as chemical and corrosion resistance, humidity, and water resistance to protect the primed metal before subsequent fabrication processes. The coil coating primer further must provide protection for and adhesion to the finished topcoat and maintain integrity and adhesion to the coiled stock.
Although solvent-based coil coating primers predominantly have been used in the past, economics and environmental considerations dictate that aqueous coil coating primers are most desirable for industrial use, but generally have been unsatisfactory to preclude corrosion and adequately prime the bare metal coil in addition to providing the necessary flexibility, impact resistance, adhesion to the metal coil, chemical and corrosion resistance, humidity and water resistance, and exterior durability as well as providing adhesion of the primer to the finished topcoat.
It now has been found that an aqueous coil coating primer based on a water-dispersible polyurethane polymer capable of being thermally cured in synergistic combination with a latex effectively provides an improved coil coating primer.